Carbon Dioxide Dissociation at 6000° to 11 000°K

The dissociation rate of CO₂ has been measured for temperatures from 6000° to 11 000°K. The rate of disappearance of CO₂ behind reflected shock waves in a 1%‐CO₂−99%‐Ar gas mixture was monitored by observing infrared radiation from the 2.7‐μ CO₂ combination bands. The dissociation rates expressed in classical collision theory and an Arrhenius equation are (in cubic centimeters per particle·second), respectively, $k_{\mathrm{Ar}}{\text{=(8.95)(10}}^{\text{−13}}{\mathrm{)(D/kT)}}^{\text{3.21}}\hspace{0.17em}\exp \mathrm{(-D/kT)}$ and $k_{\mathrm{Ar}}{\text{=(1.92)(10}}^{\text{−13}}{\mathrm{)T}}^{\frac{1}{2}}\hspace{0.17em}\exp \text{(−2.96\hspace{0.17em}e}\mathrm{V}\mathrm{/kT)}$ where D=5.5 eV is the CO₂ dissociation energy, k is the Boltzmann constant, and T is the absolute temperature. A rate constant was also determined from observations of the CO flame band emission at a wavelength of 3500 Å, which, at equilibrium, is proportional to the product of the CO and O concentrations. The rates determined from these measurements are about a factor of three lower than those obtained from the infrared measurements, and the process has an activation energy of 3.68 eV compared to the 2.96 eV for the infrared measurements. It is suggested that the infrared observations are a measure of the CO₂ dissociation, while the flame band emission is controlled by the recombination of CO and O into an excited CO₂ electronic energy level and the radiative life time of this CO₂ level. A summary is given of CO₂ dissociation measurements obtained with both methods over a temperature range from 2600° to 11 000°K.